Richard J. Lock

Multi-modal locomotion: from animal to application

The majority of robotic vehicles that can be found today are bound to operations within a single media (i.e. land, air or water). This is very rarely the case when considering locomotive capabilities in natural systems. Utility for small robots often reflects the exact same problem domain as small animals, hence providing numerous avenues for biological inspiration. This paper begins to investigate the various modes of locomotion adopted by different genus groups in multiple media as an initial attempt to determine the compromise in ability adopted by the animals when achieving multi-modal locomotion. A review of current biologically inspired multi-modal robots is also presented. The primary aim of this research is to lay the foundation for a generation of vehicles capable of multi-modal locomotion, allowing ambulatory abilities in more than one media, surpassing current capabilities. By identifying and understanding when natural systems use specific locomotion mechanisms, when they opt for disparate mechanisms for each mode of locomotion rather than using a synergized singular mechanism, and how this affects their capability in each medium, similar combinations can be used as inspiration for future multi-modal biologically inspired robotic platforms.

Development of a biologically inspired multi-modal wing model for aerial-aquatic robotic vehicles through empirical and numerical modelling of the common guillemot, Uria aalge

The common guillemot, Uria aalge, a member of the auk family of seabirds, exhibits locomotive capabilities in both aerial and aquatic substrates. Simplistic forms of this ability have yet to be achieved by robotic vehicle designs and offer significant potential as inspiration for future concept designs. In this investigation, we initially investigate the power requirements of the guillemot associated with different modes of locomotion, empirically determining the saving associated with the retraction of the wing during aquatic operations. A numerical model of a morphing wing is then created to allow power requirements to be determined for different wing orientations, taking into account the complex kinematic and inertial dynamics associated with the motion. Validation of the numerical model is achieved by comparisons with the actual behaviour of the guillemot, which is done by considering specific mission tasks, where by the optimal solutions are found utilizing an evolutionary algorithm, which are found to be in close agreement with the biological case.

Impact of Marine Locomotion Constraints on a Bio-inspired Aerial-Aquatic Wing: Experimental Performance Verification

This paper describes the design, fabrication, experimental testing and performance optimization of the morphology of a flapping wing for use on a robot capable of aerial and aquatic modes of locomotion. The focus of the optimization studies is that of wing design for aquatic propulsion. Inspiration for the research stems from numerous avian species which use a flapping wing for the dual purpose of locomotion (propulsion) in both air and water. The main aim of this research is to determine optimal kinematic parameters for marine locomotion that maximize nondimensionalized performance measures (e.g., propulsive efficiency), derived from analysis of avian wing morphing mechanisms that balance competing demands of both aerial and aquatic movement. Optimization of the kinematic parameters enables the direct comparison between outstretched (aerial) and retracted (aquatic) wing morphologies and permits trade-off studies in the design space for future robotic vehicles. Static foils representing the wing in both an extended and retracted orientation have been manufactured and subsequently subjected to testing over a range of kinematics. Details of the purpose built 2 degree-of-freedom (dof) flapping mechanism are presented. The gathered results enable validation of previously developed numerical models as well as quantifying achievable performance measures. This research focuses on the mechanical propulsive efficiencies and thrust coefficients as key performance measures whilst simultaneously considering the required mechanical input torques and the associated thrust produced.

Development of a biologically inspired multi-modal wing model for aerial-aquatic robotic vehicles

This paper presents a numerical model of a morphing wing supporting the development of a biologically inspired vehicle capable of aerial and aquatic of locomotion. The model draws inspiration from the seabird Uria aalge, the common guillemot. It is implemented within a parametric study associated with aerial and aquatic performance, specifically aiming at minimizing energy of locomotion. The implications of varying wing geometry and kinematic parameters are investigated and presented in the form of nested performance charts. Trends within both the aquatic and aerial model are discussed highlighting the implications of parameter variation on the power requirements associated with both mediums. Conflicts of geometric parameter selection are contrasted between the aerial and aquatic model, as well as other trends that impact the design of concept vehicles with this capability. The model has been validated by implementing a heuristic optimization of its key parameters under conditions akin to those of the actual bird; optimal parameters output by the model correlate to the actual behaviour of the guillemot.

The effect of aerodynamic braking on the inertial power requirement of flapping flight: case study of a gull

There has been an unresolved question of whether there is any significant degree of aerodynamic braking during wing deceleration in the flapping flight of birds, with direct analogies existing with flapping micro air vehicles. Some authors have assumed a complete conversion of kinetic energy into (useful) aerodynamic work during wing deceleration. Other authors have assumed no aerodynamic braking. The different assumptions have led to predictions of inertial power requirements in birds differing by a factor of 2. Our work is the first to model the aerodynamic braking forces on the wing during wing deceleration. A model has been developed that integrates the aerodynamic forces along the length of the wing and also throughout the wing beat cycle. A ring-billed gull was used in a case study and an adult specimen was used to gather morphometric data including a steady state measurement of the lift coefficient. The model estimates that there is a 50% conversion of kinetic energy into useful aerodynamic work during wing deceleration for minimum power speed. This aerodynamic braking reduces the inertial power requirement from 11.3% to 8.5% of the total power. The analysis shows that energy conversion is sensitive to wing inertia, amplitude of flapping, lift coefficient and wing length. The aerodynamic braking in flapping micro air vehicles can be maximised by maximising flap angle, maximising wing length (for a given inertia), minimising inertia and maximising lift coefficient.

Quantification of the benefits of a compliant foil for underwater flapping wing propulsion

This paper presents results detailing the performance of a flexible wing for use on a vehicle capable of both aerial and aquatic modes of locomotion, with primary focus on the aquatic substrate. The motivation for the research stems from the ability of avian species within the natural world demonstrating this multi-modal capability, utilsing a flapping mechanism as a means of propulsive generation. The fundamental aim is to capture the beneficial traits of a flexible wing and quantify any potential improvements in performance. We present a simplified numerical model which acts as an initial design tool prior to the fabrication of a flexible wing. This model aids in wing geometry selection so that under key kinematic parameters the wing passively deforms during aquatic operations in a beneficial manner, in an attempt to increase the maximum lift coefficient of the foil. Using the model we have fabricated a flexible wing and experimentally evaluated its performance in a range of tests, varying kinematic parameters relating to the flapping motion and forward velocities and compared this with a rigid wing model to investigate if the passive chord-wise flexibility leads to an increase in propulsive efficiency. We present the initial data set making this comparison, showing that the flexible wing was found to exhibit higher propulsive efficiencies at specific kinematic parameter sets. This modeling and experimental study will provide a foundation for the design of future vehicles capable of swimming and aerial locomotion, and help quantify the benefits of passively compliant structures in flapping wing propulsion.

Morphing Modes Of Mobility In Natural AndEngineered Systems

Autonomous vehicle utility has reached a plateau due to mobility constraints on the current generation of units in the field. Of particular note is the inability of existing robotic systems to manoeuvre in more than one substrate (e.g. land, air, water). Although no mature engineering examples exist today, many animals possess this capacity. Utility for robots often reflects a similar design space as small animals; multiple locomotion modes would represent a generational leap in their capability. Flight could allow a vehicle to approach a general target area, while crawling or swimming locomotion would enable otherwise unachievable tasks (e.g. close inspection, surveillance, sampling, etc.). The goal of our research is to develop a scalable architecture, drawing on inspiration from nature, for autonomous systems with the capacity for morphing modes of mobility. While much research has been performed into biological mechanisms of locomotion in a single medium, the tradeoffs, potential synergies, and basic measures of performance supporting natural mobility in several substrates has yet to be rigorously investigated from a design perspective. In this work we report modelling of the functional, physical, and operational architectures for a candidate set of animals with multiple modes of locomotion, with specific focus on the scalability of avian designs. Modelling of key parameters is used to demonstrate their effectiveness under specific engineering measures of performance. In the longer term, this work is envisaged to provide a foundation upon which to base the design of robotic systems capable of multiple modes of mobility as well as to analyze morphing locomotion modes in nature

A Bio-inspired Condylar Knee Joint For Knee Prosthetics

This paper presents a novel bio-inspired condylar prosthetic knee joint developed at the University of Bristol. The bio-inspired condylar joint mimics the structure and biomechanics of the human knee joint. The joint contains an inverted parallelogram four-bar mechanism combined with a cam mechanism. The joint has a favourable mechanical advantage compared with a hinge joint. The joint is also compact and robust. An adultsized prototype joint has been designed and tested. The prototype joint contains a long cable for the ligaments with a mechanism for adjusting preload. Compared with other prosthetic joints, the condylar joint has the advantages that it is simple and closely mimics human biomechanics. This paper presents the design of the new artifi cial knee joint and some of the test results. The joint can be used in artifi cial legs and also for knee implants. A rapid prototyping procedure is also presented that enables a custom-sized prosthetic knee joint to be made very quickly and from just a few key dimensions. This process has the potential to improve the quality of surgical implants.

The Energy Benefits of the Pantograph Wing Mechanism in Flapping Flight: Case Study of a Gull

Bird wings generally contain a 4-bar pantograph mechanism in the forearm that enables the wrist joint to be actuated from the elbow joint thus reducing the number of wing muscles and hence reducing the wing inertia and inertial drag. In this paper we develop a theoretical model of inertial power for flapping flight to estimate the advantage of the 4-bar pantograph mechanism by comparing the inertial power required for the case where wrist muscles are present in the forearm with the case where wrist muscles are not present in the forearm. It is difficult to predict how wrist muscles would look when there is no pantograph mechanism. Therefore a lower bound and upper bound case are defined. The lower bound case involves redistributing the elbow muscles with no increase in wing mass. The upper bound case involves replicating the biceps-triceps muscles near the wrist joint. At minimum power speed the model estimates that the 4-bar pantograph mechanism reduces the inertial power for the gull from between 6.1%–12.3% and reduces the overall power by 0.6%–1.2%. When account is taken of the tight margins involved in the design of a flying vehicle, the energy savings produced by the pantograph mechanism are significant. A ring-billed gull was chosen for the case study and an adult specimen was obtained to gather morphometric data. Lessons for the design of flapping micro air vehicles are discussed.